Diet restriction (DR) is known to prolong life, decrease disease including cancer, and substantially enhance quality of life. Objective of our studies was to investigate the effect of moderate DR (65 percent of ad libitum, AL food consumption), on acute toxicity of a model hepatotoxicant, thioacetamide (TA). Male Sprague-Dawley rats maintained on DR for three weeks were challenged with an ordinarily lethal dose of TA (600 mg/kg, ip). Seventy percent of the DR rats survived in contrast to only 10 percent of the AL rats. Paradoxically, mechanism-based liver injury of TA was approximately two-fold higher in the DR rats compared to the AL rats. Additional investigations revealed that compensatory tissue repair was higher and sustained longer in DR rats, enabling them to restore liver structure and function and to survive. DR rats treated with a low dose of TA (50 mg/kg, ip) had six-fold higher liver injury as the AL rats, nearly equal liver injury as the AL rats receiving a 12-fold higher dose. Compensatory tissue repair was much higher in the DR rats. All low dose rats of both groups recover. While only 10 percent of the AL rats recover, 70 percent of the DR rats recover from the high dose. Two major questions arise. 1) What is/are the mechanism(s) of higher liver injury in DR rats? 2) What are the molecular mechanisms underlying the stimulated compensatory tissue repair that enable the rats to overcome normally lethal liver injury? Preliminary results suggest that CYP2E1 mediates the mechanism- based bioactivation of TA and DR-induced increase in CYP2E1 is likely to be the dominant mechanism of highly increased TA liver injury. While the emphasis will be placed on the second question, we propose to complete answering the first question as well. Objectives of this proposal are to test our hypotheses: 1. TA is predominantly bioactivated by CYP2E1 and DR-induction of CYP2E1 is the dominant mechanism for highly increased mechanism-based liver injury of TA. II. Pro-inflammatory cytokines (TNF-alpha, IL-6), nuclear transcription factors (NFkB, STAT3), growth factors (TGF-alpha, HGF), and their receptors (EGFR, c-met) working through MAPK-Ras pathway are responsible for gene activation fos, c-myc, c-jun, ha-ras) for higher mitogenic response in DR rats providing new cells for compensatory tissue repair. The proposed studies will test specific testable hypotheses through specific, focused experiments including the use of gene knockout models. The findings will shed light on the mechanisms of protection afforded by moderate DR against toxicity of environmental agents that have the potential to impact environmentally induced liver diseases.